Butadiene-styrene copolymer tackified with isoolefin-diolefin-styrene copolymer



Patented Feb. 14, 1950 BUTADIENE-STYRENE COPOLYMER TACK!- FIED WITHISOOLEFIN-DIOLEFIN-STY- RENE COPOLYMER Stewart S. Kurtz, Jr., Merion,Pa., assignor to Sun Oil Company, Philadelphia, Pa., a corporation ofNew Jersey No Drawing. Application May 26, 1945, Serial No. 596,099

3 Claims. (Cl. 260-455) This invention relates to the use of synthetichydrocarbon compositions prepared by polymerization of a three-componentmixture comprising an iso-olefln of 4 6' carbon atoms having a doublebond in the alpha position and a side chain in the beta position, analiphatic 1,3-conjugated diolefin and an aryl-substituted vinylcompound. In its broader and more general aspects, the inventioncontemplates the preparation and the compounding with a synthetic rubberhaving aromatic rings in the molecules thereof of a variety of syntheticcompositions differing to an extent in properties and characteristics.More particularly, the invention is concerned with the preparation ofsynthetic compositions having regulable plasticity and tackcharacteristics followed by compounding of the compositions with asynthetic rubber, as defined. This application is a continuation-inpartof Serial No. 487,817, filed May 20, 1943, now abandoned.

Within the overall scope of the invention, specific synthesis may entailthe use of different specific hydrocarbon source material components asto each of the aforesaid three types which are to be present in anygiven polymerization operation. As to the required diolefin and arylcomponents, respectively, these may be selected with reasonable freedomof choice from the indicated classes of compounds. The permissiblevariance in the cleflnic component of a given reaction mixture is morelimited. I

The attainment of the desired characteristics in the synthetic productsis brought about by the proper choice of operating variables within thelimits hereinafter defined. Of particular importance as factorscontrolling the nature and character of the compositions, are the ratiosof monomeric components, the type and quantity of catalyst, thepolymerization temperature and ample, elastomers comprisingbutadiene-styrene copolymers prepared by the conventional emulsionpolymerization process lack the tack or cohesiveness of natural rubber.Milling natural rubber causes an increase in tack and plasticity,whereas milling butadiene-styrene copolymers is not effective to thedesired degree. Moreover, since they fail to soften or break down well,the butadiene-styrene copolymers are difficult to mill and also toprocess further after milling. Thus they are difficult to friction orcalender into fabrics such as the cord fabrics used in the manufactureof tire carcasses, and they fail to perform properly in tubingoperations as employed in manufacturing tire treads unless largequantities of softener, etc., are added.

It is believed by some authorities that natural rubber consists of gelrubber of relatively high molecular weight and poor solubility inbenzene, petroleum ether or like solvents, and "sol rubber of relativelylow molecular weight and good solubility in such solvents. The solcomponents of natural rubber are regarded as eifec: tive in impartingtack and plasticity thereto. On milling natural rubber both the tack andplasticity increase due to the formation of more low molecular weightfragments. On the other hand, butadiene-styrene synthetics appear to bemade up of copolymers having a fairly uniform, high molecular weight,and thus to be deficient in lower molecular weight componentscorresponding to sol rubber. Milling the butadiene-styrene copolymersapparently fails to produce enough of the low molecular weightcomponents to impart the desired tack and plasticity.

The present invention is based on the discovery that it is possible tocopolymerize a threecomponent hydrocarbon mixture, including aniso-olefin of 4-6 carbon atoms having a double bond in the alphaposition and a. side chain in the beta position, an aliphatic1,3-conjugated diolefin and an aryl-substituted vinyl compound,

in proportion, manner and under conditions such come certain prior artdisadvantages referred to herein. Unless the proportions, manner andconditions, hereindefined are employed, the products may varyconsiderably in character, ranging from a type resembling a viscous,sticky oil to a type resembling a hard thermoplastic resin. However, byfollowing the prescriptions of the present invention a particularlyuseful intermediate type comprising vulcanizable rubbery materials orelastomers is obtained. Through proper adjustment of manufacturingconditions, these rubber-like products may be obtained either asrelatively low molecular weight elastomers having properties andcharacteristics similar to those attributed to sol type" rubber, or asrelatively high molecular weight elastomers whose characteristicsapproach those attributed to the gel type."

I have discovered that synthetic rubber oi the butadiene-styrene typemay be improved with respect to tack, plasticity and effective responseto milling, and that such attributes may be regulated and controlled, byadjusting the proportion of relatively low molecular weight componentsin such synthetic rubber. This adjustment may be accomplished by addingto the butadiene-styrene copolymers the relatively low molecular weightelastomers of this invention, which are compatible with thebutadiene-styrene copolymers and which accordingly impart desiredcharacteristics to the synthetic rubber material being manufactured.

In order for two difierent types of elastomers to be suitable forcompounding and vulcanizing together, two primar requirements should bemet. Specifically, the different copolymers first should be physicallycompatible and secondly should be chemically compatible with respect tocuring rate, 1. e. should have approximately the same rate of cure. Inorder to meet the first requirement there must be sufllcient similarityin the molecular structures of the two types of elastomers to ensurephysical homogeneity of the vulcanized blend. Lacking such similarity,the copolymers on compounding and curing will fail to produce ahomogeneous product. The second requirement is of importance in orderfor the two types of elastomers to have the same state of cure in thevulcanized product. With substantially diflerent rates of cure, there isdanger that the faster curing type of elastomer may become scorchedbefore the other is cured sufliciently. By way of illustration of thesetwo types of compatibility, so-called butyl rubber, which comprises thecopolymers of isobutene and a small proportion of another unsaturatedhydrocarbon such as butadiene, has a chemical structure sufficientlysimilar to that of natural rubber to be physically compatible therewith.However, butyl rubber possesses such a low degree of unsaturation thatit cures at a much slower rate than natural rubber and for this reasonis not suitable for compounding with the latter. n the other hand, butylrubber is sufflciently different in chemical structure frombutadiene-styrene copolymers to be physically incompatible therewith,and also has such a low degree of unsaturation as to be incompatiblewith respect to cure. As further illustration, butadiene-styrenecopolymers and natural rubber are compatible as to rate of cure, but areincompatible physically due to the dissimilarity in molecular structurecaused by the presence of aromatic rings but no methyl groups in thecase oi. the butadiene-styrene copolymers in contrast to methyl groupsbut no aromatic rings in the case of natural rubber.

An outstandin advantage of the present invention is that both molecularstructure and cure rate of the elastomer product is varied to correspondto the molecular structure and cure rate of the synthetic rubber withwhich it is blended. These variations may be accomplished by varying theproportions of the three monomeric constituents from which theelastomers are prepared. Thus, the ratio of alkyl side chains to chaincarbon atoms in the product may be regulated by varying the proportionof iso-olefln used, the ratio of aryl side chains to chain carbon atomslikewise may be regulated by varying the proportion of the arylcompound, and the inherent curing rate may be controlled by adjustingthe diolefin content so as to provide the desired degree oiunsaturation. In applying the invention to the production of elastomerssuitable for compounding with budadiene-styrene synthetics, the monomercontaining an aryl group should be used in sufficient proportion toprovide an aromatic ring content somewhat near that of thebutadiene-styrene copolymers in order to ensure physical compatibility,and sufiicient diolefin should be used to give a corresponding rate ofcure.

According to this invention there is provided a method of tackiiying andplasticizing a synthetic rubber having aromatic rings in the moleculesthereof, which comprises formin a tackifier product characterized bytacky, elastic properties, by the presence of suflicient double bonds toimpart to the product a chemical compatibility with said syntheticrubber in respect 01' rate ofcure and by the presence of sufficientaromatic rings to impart compatibility with said synthetic rubber inrespect of physical homogeneity on curing therewith, by copolymerizing amonomeric mixture comprising from about 50 to about '70 parts by weightof an isoolefin of 4-6 carbon atoms having a double bond in the alphaposition and a side chain in the beta position, from about 10 to about30 parts by weight of an aliphatic 1,3-conjugated diolefin and fromabout 20 to about 30 parts by weight of an aryl-substituted vinylcompound, said copolymerization being effected at a temperature of fromabout -40 C. to about 160 C. with the ald of a polymerization catalyst,adapted to copolymerize said monomers at said temperature; correlatingthe proportion of said monomers in the monomeric mixture and thepolymerizing conditions within the limits defined herein with atackifier having said characteristics, eifecting said polymerization toform said tackifier product; separating said product from the reactionmixture; and milling together a major proportion of said syntheticrubber and a minor proportion of said tackifier product thereby toimpart tack and plasticity to the synthetic rubber blend.

The general procedure of preparing the copolymers employed in thisinvention comprises cooling a mixture of an isoolefin as defined hereinwhich preferably is iso-butene, an aliphatic 1,3-conjugated diolefinsuch as butadiene or isoprene, and an aryl-substituted vinyl compoundsuch as styrene to a sub-zero temperature which may be as low as orlower than minus C., preferably although not necessarily in the presenceof a diluent, and subjecting the cooled mixture to the catalytic actionof a Friedel- 76 Crafts type catalyst. Copolymerization of the monomerstakes place rapidly with the liberation of heat, and means must beprovided for absorbing the heat generated. This can be done mostconveniently by employing a material such as a liquefied, normallygaseous hydrocarbon as diluent, and allowing it to vaporize and thus actas a refrigerant. After polymerization, the diluent and any unreactedmonomers or low boiling reaction products are separated from thecopolymers which have been formed. It is often desirable to add apetroleum fraction of lubricating oil consistency just before makingthis separation, as more particularly explained hereinafter, in whichcase the separated product will be a homogeneous mixture of copolymersand petroleum hydrocarbons. The product, comprising either copolymers ora mixture of copolymers and petroleum hydrocarbons as the case may be,is treated to destroy any admixed catalyst which, otherwise, might causeadditional polymerization. Th's may be accomplished by mixing arelatively small proportion of water with the product and boiling offthe water, there by to hydrate the catalyst and yield a finishedcopolymer product. It also may be accomplished by stirring thecopolymers with a large proportion of water in order to hydrate thecatalyst and at the same time wash out the products of hydration,settling the resulting mixture at elevated temperature, and separatelywithdrawing the copolymer layer.

The solubility in the reaction mixture of the copolymers formed onpolymerization depends largely on their molecular weight. Generally, lowmolecular weight copolymers tend to be soluble and to remain in solutionafter polymerization whereas copolymers having higher molecular weightsare insoluble and therefore settle out as either a plastic or granularmass. Under some conditions a major portion of the copolymers separatesfrom solution while in other cases all of the copolymers remain insolution, depending on the particular operating conditions employed andthe type of material obtained. The copolymers therefore can be separatedinto fractions of high and low average molecular weights, if desired, byseparating the solution from the insoluble material, the low molecularweight fraction being obtained from the separated solution byevaporation of the diluent and any other low r boiling material such asunreacted monomers. This difference in solubility may be utilized toobtain two fractions differing in characteristics if desired. On theother hand, the operating conditions may be adjusted so as to give asingle product, which may contain both relatively high and relativelylow molecular weight materials but which has an average molecular weightsuch that the product has the characteristics desired. The exactprocedure and conditions to employ for any specific synthesis depends onthe particular type of product desired. Of primary importance indetermining the nature and character of product is, of course, thecomposition, which is controlled by varying the proportions of monomericconstituents. However, for any given composition, productcharacteristics may be varied to considerable extent by varying thedegree of polymerization and thus the product molecular weight. Withinreasonable limits of composition, the average molecular weight is arough measure of the nature and character of product obtained, and ithas been found to be controlled largely by the following processingvariables: I

1) Monomer ratios in the charge (2) Purity of the monomers and diluent(3) Polymerization temperature (4) The type and quantity of catalyst em-5 ployed.

These are discussed in detail below but in general it may be stated thathigh molecular weight is favored by low temperature and pure compomnents.

In the preparation of the copolymers employed in this invention,isobutene is preferred as the iiz-mono-olefinic component; however.other polymerizable iso-mono-oleflns also may be used. In order toensure suflicient capacity for polymerization, the mono-olefiniccomponent should have the double bond in the alpha position and a sidechain in the beta position as for example, 2 methyl-l-butene,2-ethyl-1-butene, 2,3 dimethyl-l-butene, or the like. Moreover,isoolefins of relatively high molecular weight, even though having thespecified molecular structure, may be too unreactive to be of use in thesynthesis of these novel elastomers. As the conjugated diolefin, eitherbutadiene or isoprene is preferred although other dienes'such aspiperylene, conjugated hexadienes or chloroprene may be used. As thearyl-substituted vinyl compound, styrene is preferred but other arylcompounds such as substituted vinyl benzenes, vinyl naphthalene or thelike also are useful.

The proportions of monomeric ingredients may be varied considerably, andsuch variation is of major importance in predetermining the productcharacteristics. For tackifier products the proportions generally mayvary within the following ranges: from about 50 toabout 70 parts ofisobutene, from about-l0 to about 30 parts of butadiene and from about20 to about 30 parts of styrene. A relatively low isobutene contenttends to cause the formation of thermoplastic products rather thanelastomers. Increasing the butadiene content tends to decrease molecularweight and increase softness and tack provided the isobutene content isnot too low; however at relatively low isobutene contents, say

below 50% isobutene, increasing the proportion of butadiene at theexpense of the isobutene tends to cause increased hardness, decreasedtack and at sufficiently low isobutene content the for mation ofthermoplastic materials, apparently through cross-linking of molecules.Increasing the styrene content when a relatively small proportion ispresent also has the effect of decreasing molecular weight andincreasing softness and tack to a minor extent, but at higher styrenecontents causes a decrease in tack, an increase in apparent tensilestrength of the 'uncured copolymer and a tendency toward the formationof thermoplastic rather than rubbery products. The following areparticularly suitable formulas (given in parts by weight) for makingtackifiers (iii of varying character for butadiene-styrene syntheticrubber:

It is noted that analysis of the copolymer products by the best meansnow available indicates that the monomers on polymerization combine inat least nearly the same proportions as present in the charge. From thisit might be inferred that the total yield of copolymers would berelatively independent of composition, and such has been found to be thecase. The total yield of copolymers does show some variation, the yieldusually ranging from about 70 per cent to about 98 per cent when adiluent is employed, but this appears to be due to variations inoperating conditions such as rate of addition of catalyst, total time ofpolymerization or other factors relating to loss of monomers throughevaporation and not to composition variations to any appreciable extent.However the yield of relatively high molecular weight copolymers, incontrast to yield Composition of charge Yield of insoluble elastomers,Parts of Parts of Parts of per cent isobutene butadiene styrene oncharge Here, an increase in butadiene content from 10 parts to 30 partscaused the yield to drop from 71 per cent to 35 per cent. On the otherhand, an increase in the styrene content while holding the butadienecontent constant has an almost negligible effect on the yield, asillustrated by the following data:

Composition of charge Yield of insoluble elastomers, Parts of Parts ofParts of pot cent isobutene butadiene styrene on charge In this case anincrease in styrene content from parts to 30 parts caused the yield todecrease only from 71 per cent to 69 per cent. It therefore isdesirable, in manufacturing the insoluble or higher molecular weighttype elastomers, to use as small a proportion of butadiene as would beconsistent with obtaining the characteristics desired, in order toeffect a high yield. On the other hand, the styrene content of thecharge may be selected only on the basis of the characteristics impartedto the product and without regard to yield.

The presence of impurities in the monomers and diluent usually tends tocause the formation of the low molecular weight type of elastomers. Inparticular, the presence of substantial amounts of straight chainolefins having more than two carbon atoms results in a lower averagemolecular weight of the product. The presence of various otherimpurities such as sulfur compounds or phenolic constituents also causeslower molecular .used to supply this component.

weights. Saturated paraflin hydrocarbons appear to have no efiect onmolecular weight. It should be understood, however, that the tendencyfor impurities to cause low molecular weight does not necessarilymeanthat pure components must be used in order to obtain useful elastomertype products. for the effect of even extremely large amounts ofimpurities in many cases may be compensated for by appropriateadjustment of other operating conditions. For instance, it has beendiscovered that a refinery C4 fraction containing about 8 per centbutene-l, about 11 per cent butene-2 and only about 8 per cent isobutenemay be used to supply the necessary isobutene content of a reactionmixture and that under suitable polymerization conditions a very goodtackifier of the soft, sticky type may be obtained. Other C4 fractionswhich contain appreciable although minor proportions of butadienelikewise may be The fact that such impure components are at timespermissible is of decided economic advantage.

The temperature at which the polymerization reaction is carried out hasa pronounced efiect on molecular weight of the product, the higher thetemperature the lower being the average molecular weight for any givencombination of monomers. At relatively high temperatures, such as sayminus 20 C., the copolymer products usually are of sufficiently lowmolecular weight to have the appearance of sticky, viscous olls ratherthan elastomers or thermoplastic materials. At lower temperatures eitherrubbery or thermoplastic materials may be obtained.

As mentioned above, the preferred means of controlling the temperaturecomprises the addition of a diluent which by evaporating acts as aninternal refrigerant. Usually 2-4 parts by weight of such diluent areused for each part of monomers in the reaction mixture. Various light,normally gaseous hydrocarbons are suitable diluents since they are inertand have the capacity for dissolving the monomers in required amounts.The particular hydrocarbons which may be employed and their boilingpoints are a follows:

C. Methane -161 Ethylene -104 Ethane -88' Propane -42 temperature may bemaintained at one of the various temperature levels within the range ofabout minus 40 C. to about minus C.

The lower the boiling point of the diluent used for any given ratio ofmonomers, the greater is the tendency toward the formation of tougherand less tacky products containing smaller proportions of low molecularweight copolymers. For example, with an isobutene:butadiene:styreneratio of 60:20:20 and boron fluoride as the catalyst, propane as diluentunder atmospheric pressure results in a soft and very tacky product,ethylene as a diluent results in a rather tough elastomer product havingmuch less tack and a considerably smaller proportion of low molecularweight copolymers, and ethane as a diluent gives a product ofintermediate average molecular 7 weight and properties. It should benoted, however, that for any given temperature the product molecularweight and properties will vary considerably with the monomer ratios,and thus that it is possible by appropriate selection of chargecompositions to obtain a product at some particular polymerizationtemperature that is substantially identical as regards plasticity andtack with a product obtained at another temperature. For instance, theproduct obtained from an isobutene: butadienezstyrene composition of40:50:10 with propane as diluent evaporating under atmospheric pressureis very much like the product obtained from a composition of 50:30:20with propane as diluent but cooled to minus 78 0., both products beingrather tough but sticky elastomers. Obviously, however, the two productswould differ in cure rate due to different degrees of unsaturation ofpropane, ethane or ethylene with appropriate selection of catalyst andproportions of ingredients permits sufilcient variance of productcharacter. v v

The ease with which the temperature is controlled is not the onlyadvantage resulting from the use of a diluent. Of possibly even moreimportance is the effect on the yield of elastomers: for a verysubstantial increase in the total amount of copolymers formed resultsfrom the use of a diluent. Total yields of 70-98 per cent based on theweight of monomers usually are obtained when a diluent is employed,whereas yields of only about 50 per cent are obtained under similarconditions but'without a diluent.

There is a difference in the character of insoluble elastomers formed onthe one hand with ethane and on the other hand with ethylene as diluent.In the case of ethane the copolymers precipitate as a tacky plasticmass, whereas with used in excessive amounts may result in theforethylene the precipitated copolymers are granular and haveconsiderably less tack. This mav be due to the difference in temperatureobtained with the two diluents or possibly to the formation of a looselycombined complex of ethylene and boron trifiuoride which results in anincrease in concentration of effective catalyst present in the liquidphase. There is evidence that the ethylene in spite of its unsaturationis inert with respect to the polymerization reaction.

Although ethylene apparently is inert in the reaction mixture,propylene, on the other han v appears to take part in thecopolymerization and acts as a, chain breaker." thereby preventin theformation of long chain molecules of hi h molecular weights. Thus, ithas been found th t when a crude grade of propane containing abo"t 20per cent propylene was used as the diluent under certain operatingconditions, the co olv- 10 or the reaction mixture may be sprayed into avessel containing the gaseous boron fluoride. However, when ethylene isused as the diluent, it is preferable to dissolve the boron fluoride inan additional amount of ethylene and inject the thus formed solution ofcatalyst into the reaction mixture. This method of adding the catalystsimplifies theregulation of the addition rate and thus facilitatescontrol of the rate of reaction. In addition to boron fluoride, aluminumchloride is also an effective catalyst. When the latter is used,however, it first must be dissolved in a suitable solvent, such as ethylchloride, and the solution then injected into the reaction mixture. Forthe economic production of elastomers, it is essential that the ethylchloride be recovered and reused; and since this presents considerabledifflculty and necessitates an additional operating step, it is moreconvenient to use boron fluoride. Another advantage in using boronfluoride is that excessive amounts may be employed without impairing thequality of elastomer product obtained. Aluminum chloride is in somerespects a more vigorous polymerizing catalyst than boron fluoride and,consequently, more diflicultly controlled and if mation of brittlethermoplastic products rather than elastomers. The catalytic eifects ofboron fluoride and aluminum chloride seem to be more nearly equal atabout minus C. than at minus 40 C. Various other Friedel Crafts typecatalysts are known to be effective in promoting low temperaturepolymerization reactions and it is tobe understood that these might beemployed without departing from the scope of this invention. ByFriedel-Crafts type catalysts is meant halides of the amphoteric metalsincluding particularly BF3, A101: and SnCh. Corre- -sponding halogenacid addition compounds such.

as HBF4 and HzSnCls also may be used but are not preferred.

The low molecular weight type of elastomers are extremely tackymaterials which have a tendency to stick to-the sides of the reactionvessel and, consequently, considerable diiiiculty often is experiencedin withdrawing these materials and in the subsequent blending andcompounding with butadiene-styrene synthetics. In

order to obviate such difficulty a petroleum fraction of lubricating oilconsistency may be added to the reaction mixture after thepolymerization has been completed but before the diluent has beenremoved. as. mentioned hereinabove. On evaporation of the diluent andany unreacted monomers a homogeneous mixture of elastomers and suchpetroleum fraction thereby may be obtained as product, This product.which has the appearance of a very viscous oil at ordinarytemperatureson warming becomes relatively fluid and then may be handledwithout difiiculty. Furthermore, it has been-found that by employing aspecific type of petroleum fraction. a petroleum hydrocarbon-elastomerproduct may be obtained which is an excellent tackiiior and plasticizerfor butadiene-styrene copolymers. The type of petroleum fraction requred for this purpose is one which frequently is used in the arts as asoftener or plasticizer in the compounding of rubber, both synthetic andnatural. Such softeners or plasticizers are derived from a naphthenebase crude petroleum and preferably have a Saybolt Universal viscosityof about -160 seconds at 100 F.

76 Petroleum fractions from sources other than accuse naphthenic crudesgenerally fall to have suflicient compatibility with rubber to be ofutility in applications of this type. A petroleum fraction, which iswell known in the rubber industry as "Circo light processing oil," anaphthenic base oil having a Saybolt Universal viscosity at 100 F. of150-160 seconds and an A. P. I. gravity of 20.2-22.5 at 60 F., and whichis listed on page 310 of the Rubber Red Book, 1941 edition, is anexample of the type of petroleum-derived softener or plasticizerpreferred. Such softeners or plasticizers do not impart any substantialamount of tack to the butadiene-styrene type of synthetic rubber onbeing compounded therewith but merely act as plasticizing or softeningagents. The viscous oily products obtained by using such specificpetroleum fraction in the manner described above, however, may be usedto impart both tack and plasticity or softness to the butadiene-styrenetype of synthetic rubber. The tack and plasticity may be regulated asdesired in the blend by varying the ratio of petroleum fraction toelastomers in these tackifler products and/or by varying the proportionof the tackifier incorporated with the butadienestyrene synthetic. Inpreparing products of this type, it generally is preferable to addenough of the specified petroleum fraction to the reaction mixture afterpolymerization to give a product containing 25-50 per cent petroleumhydrocarbons, although larger or smaller proportions may be desirable attimes. The product may be blended with butadiene-styrene copolymers inwidely varying proportions, depending on the tack and plasticity desiredin the finished blend. A proportion of about 20-30 parts of tackiilerproduct to 70-80 parts of butadiene-styrene copolymers is preferred inmaking tire carcass stock, while a proportion of -20 parts to 80-90parts of butadiene-styrene copolymers is preferred for tread stock. Incompounding the elastomers prepared without the addition of apetroleum-derived softener or plasticizer, as much as parts ofelastomers to parts of butadiene-styrene copolymers often are desirable,particularly in the preparation of hose type stocks.

The following examples, in which parts are by weight, illustrate variousembodiments of the invention:

Example I Three hundred parts of technically pure propane (containing nopropylene) were charged as a pre-cooled liquid to a reaction vesselprovided with a mechanical stirrer. A mixture of parts of isobutene, 10parts of butadiene and 20 parts of styrene was added to and mixed withthe propane, and the temperature of the resulting mixture was adjustedto minus 78 C. and maintained approximately at this level by means ofDry Ice. While the mixture was being vigorously stirred, gaseous boronfluoride, diluted with nitrogen, was bubbled slowly therein to effectpolymerization of the monomers. The addition of the catalyst wascontinued until the reaction apparently had stopped as judged bycessation of heat evolution. The lower molecular weight elastomersremained in solution while those of higher molecular weight precipitatedas a plastic mass. Fifty parts of the petroleum fraction known as Circolight processing oil, referred to hereinabove, andhaving a S. U.viscosity of about 155 seconds at 100 F. was added to the mixture, whichthen was heated sulllciently to evaporate the propane and any unreactedmonomers. A residue comprising a homogeneous mixture of parts ofelastomers and 50 parts of petroleum hydrocarbons and containing a smallamount of catalyst was obtained. Ten parts of water were mixed with theresidue, and the mixture was heated sufflciently to drive of! the water.This destroyed the catalyst and yielded a finished elastomer productwhich was extremely viscous at room temperature.

The elastomer product or tackifler thus obtained was compounded with abutadiene-styrene copolymer, known in the trade as "Hycar 08-30," andother ingredients according to the following formula:

Parts Butadiene-styrene rubber 80 Elastomer product 20 Zinc oxide 5Medium thermal carbon black 40 Sulfur 1% Cyclohexyl amine salt ofmercapto-benzothiazole 1% This blend was placed on fabric in a mold andcured at 290 F. for 45 minutes. On testing the cured blend for adhesionto the fabric, a value of 8 pounds per linear foot was obtained. Asimiliarly compounded and cured blend, containing 100 parts of "Hycar08-30 but none of the elastomer product, had an adhesion of only 3pounds per linear foot.

Example I! A pre-cooled mixture comprising 70 parts of isobutene, 10parts of butadiene, 20 parts of styrene and 300 parts of crude propanecontaining approximately 20 per cent propylene was charged to a reactionvessel under atmospheric pressure. The propane was allowed to evaporate,thus acting as an internal refrigerant and thereby maintaining thetemperature at approximately minus 40 C. Boron fluoride was bubbled intothe mixture until no further heat evolution was evident. In this caseall of the copolymers formedwere of sumciently low molecular weight toremain in solution. Twenty-five parts of Circo light processing oil wereadded and the propane and any unreacted monomers were boiled oil,whereby a viscous homogeneous mixture comprising parts of elastomers and25 parts of petroleum hydrocarbons was obtained. The catalyst washydrolyzed and the product dehydrated as in Example I.

Two blends of the elastomer product and "Hycar 0S-30 were made, onehaving 20 parts of elastomer product blended according to the formulagiven in Example I and the other differing only in that 10 parts ofelastomer product and 90 parts of Hycar 08-30" were used. After curingon fabric at 290 F. for 45 minutes, the blends were found to have thefollowing adhe sions:

Adhesion, lbs.

per linear foot Blend containing 10 parts of elastomer product 7 Blendcontaining 20 parts of elastomer product 15 Example II! l3 processingoil in place of the tackifler and also two blends containing neithertackifler nor Circo light processing oil were compounded and'cured inlike manner. parts by weight, were used:

Both of the blends containing the tackifier milled considerably betterthan any of the other blends, tl is being true even of the blendcontaining only 10 parts of tackiiier as compared with the onecontaining 20 parts of softener; The following test data were obtainedon the blends after curing:

Blends contain- Blends contain- Blend con ing tuokifier ing softenertaining no teckiiler or softener 10 20 10 20 Parts Parts Parts PartsTensile strength.

lbs.lsq. in .r.. 2, 590 2. 240 1. 780 1.830 L280 Percent elongation 475470 505 410 470 Modulus at 300%. l. 240 9435 750 1. 050 550 Shorehardness. 55 50 48 As shown in the above tabulation, the elastomerproduct or tackifier does not cause as large a decrease in tensilestrength as the softener does. For purposes to which cured products ofthis type would be put, such large decrease in tensile strength ascaused by the softener are highly undesirable. On the other hand thetackifler has a much more beneficial effect than the softener orprocessing quality of the uncured stock.

Example IV A mixture of monomers comprising 50 parts of isobutene, 20parts of butadlene and 30 parts of styrene were cooled to approximatelyminus 70 C. by means of Dry Ice, no diluent being added in this case. Astream of boron fluoride diluted with The following formulas, showingCompound Compound without wi elastomers elastomers 5 Parts I PartsButadicno-styrene synthetic 100 g 5 5 5 50 50 Suiru 2% 254Cyclohexylamine salt of men-captobenzotbiazole 1% 1% In compoundingthese, it was 'found that the blend without elastomers could be milledonly with difllculty whereas the blend containing elastomers milled verysatisfactorily. The following data were obtained on the cured compounds:

Time of cure Tensile Per cent Shore at 290 F., strength,elongahardminutes lbs.lsq. in. tion ness 2,130 315 60 Withoutelastomers. 3: I 750 245 82 '5 1,818 280 1hthe1astomers 1,845 200 66 Acomparison of tensile strengths shows that an appreciable decrease inthis physical property with increasing time of cure occurred in the caseof blendswithout elastomers, but that the blends with elastomers had thedesirable characteristic of not exhibitingsubstantial change in tensilestrength with time of cure.

Example V A mixture comprising parts of isobutene, 30 parts of butadieneand 20 parts of styrene dissolved in 400 parts of technically purepropane was subjected to polymerization at minus 78 (3. by a procedureidentical with that of Example I except that the boron fluoride was notdiluted with nitrogen. After polymerization the propane and other lowboiling components of the poly- Butadiene-styrene rubber '15 Elastomers25 Zinc oxide 5 Phenyl naphthyl amines accelerator 1 Sulfur 1% nitrogenwas bubbled slowly into the mixture while the mixture was being stirredand the temperature was being maintained substantially at m nus C. Afterthe reaction was complete, volatile constituents in the reaction mixturewere driven off by heating. Approximately 50 parts of a moderatelyrubbery residue having extreme tack was obtained. Water was added tohydrolyze the catalyst and the wet product then was dehydrated by hotmilling.

Cycloliexyl-amine salt of mercaptobenzothiazole Medium soft carbon black50 By virtue of the presence of the elastomers, the blend milled verysatisfactorily and had good'tack and plasticity. Portions of the blendwere cured at 290 F. for various lengths of time, after which thefollowing test data were obtained:

These tests show that the cured blend satisfactorily meets requirementsfor tire carcass stock.

33 Example W A crude C4 traction having the following composition byweight:

was used to supply the isobutene'for a charge mixture having anisobutene: butadiene: styrene ratio of 60:20:20 and comprising 732 partsof crude C4 fraction, 20 parts of butadiene and 20 parts of styrene.Three hundred parts of propane were added as diluent, and the mixturewas polymerized by means of BF; at a temperature of minus 78 C.,maintained by using Dry Ice. The product, which was obtained from thereaction mixture as in previous examples, comprised 89 parts of soft,sticky elastomers suitable as a tackifler. The material was found to bepractically identical with the product obtained by polymerizing a60:20:20 mixture of pure monomers at a tem-- perature of minus 40 C.

I claim:

1. A composition of matter comprising a mixture or a'preponderantproportion of a synthetic rubber, made by polymerization of a mixtureconsisting essentially of butadiene and styrene, and a minor proportion,effective to impart tack thereto, of a tacky, elastic tackiiiercopolymer product derived by polymerization, at a temperature of fromabout --40'C. to about 160 C. with the aid of a Friedel-Crafts typecatalyst, of a monomeric mixture comprising from about 50 to about "10parts by weight of an iso-mono-olefln of 4-6 carbon atoms having adouble bond in the alpha position and a side chain in the beta position,from about 10 to about 30 parts by weight of an all- 16 phatic 1,3conjugated diolefln and from about 20 to about 30 parts by weight ofstyrene.

2. A composition of matter comprising a mixture of a preponderantproportion of a synthetic rubber, made by polymerization of a mixtureconsisting essentially of butadiene and styrene, and a minor proportion,effective to impart tack thereto, of a tacky elastic tackifler copolymerproduct derived by polymerization, at a temperature of from about C. toabout -160 C. with the aid 01 a Friedel-Craits type catalyst, of amonomeric mixture comprising from about to about parts by weight ofisobutene, from about 10 to about 30 parts by weight of butadiene andfrom about 20 to about 30 parts by weight of styrene.

3. A composition of matter comprising a mixture of a preponderantproportion of a synthetic rubber, made by polymerization of a mixtureconsisting essentially of butadiene andstyrene, and a minor proportion,effective to impart tack thereto, of a tacky elastic tackifier copolymerproduct derived by polymerization, at a temperature of from about 40 C.to about C. with the aid of a Friedel-Crafts type catalyst, of amonomeric mixture comprising from about 50 to about 70 parts by weightof isobutene, from about 10 to about 30 parts by weight of isoprene andfrom about 20 to about 30 parts by weight of styrene.

STEWART S. KURTZ, JR-

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,023,495 Thomas Dec. 10, 19352,438,340 Johnson Mar. 23, 1948 FOREIGN PATENTS Number Country Date513,521 Great Britain Oct. 16, 1936 106,371 Australia Jan. 10, 1939705,104 Germany Apr. 17, 1941

1. A COMPOSITION OF MATTER COMPRISING A MIXTURE OF A PREPONDERANTPROPORTION OF A SYNTHETIC RUBBER, MADE BY POLYMERIZATION OF A MIXTURECONSISTING ESSENTIALLY OF BUTADIENE AND STYRENE, AND A MINOR PROPORTION,EFFECTIVE TO IMPART TACK THERETO, OF A TACKY, ELASTIC TACKIFIERCOPOLYMER PRODUCT DERIVED BY POLYMERIZATION, AT A TEMPERATURE OF FROMABOUT -40*C. TO ABOUT -160*C. WITH THE AID OF A FRIEDEL-CRAFTS TYPECATALYST, OF A MONOMERIC MIXTURE COMPRISING FROM ABOUT 50 TO ABOUT 70PARTS BY WEIGHT OF AN ISO-MONO-OLEFIN OF 4-6 CARBON ATOMS HAVING ADOUBLE BOND IN THE ALPHA POSITION AND A SIDE CHAIN IN THE BETA POSITION,FROM ABOUT 10 TO ABOUT 30 PARTS BY WEIGHT OF AN ALIPHATIC 1,3 CONJUGATEDDIOLEFIN AND FROM ABOUT 20 TO ABOUT 30 PARTS BY WEIGHT OF STYRENE.